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Multiple Integrals. Ex. Ex. The bounds of the integral represent a region in the xy -plane, and the function represents a height So the integral represents the volume under the function f ( x , y ) that lies above the region R in the xy -plane. General double integral.
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The bounds of the integral represent a region in the xy-plane, and the function represents a height So the integral represents the volume under the function f (x,y) that lies above the region R in the xy-plane General double integral Iterated integral
Ex. When R is rectangular, order of integration doesn’t matter.
Ex. Find the volume of the solid bounded by the elliptic paraboloid x2 + 2y2 + z = 16, the planes x = 2 and y = 2, and the coordinate planes.
Ex. Find the average value of f (x,y) = sin x cos y over the region R = [0, ] [0, ].
To evaluate a double integral over a non-rectangular region, we need to describe the region as boundaries of x and y. Ex. Describe the region R bounded by y = 2x2 and y = 1 + x2.
Ex. Evaluate , where R is the region from the previous example.
Ex. Find the volume that lies below z = x2 + y2 and above the region D in the xy-plane bounded by y = 2x and y = x2.
Ex. Evaluate , where R is the region bounded by y = x – 1 and y2 = 2x + 6.
Ex. Find the volume bounded by x + 2y + z = 2, x = 2y, x = 0, and z = 0
Ex. Evaluate by first switching the order of integration.
Double Integrals in Polar When evaluating , it may be easier to describe R using polar coordinates.
In rectangular coordinates: dA = dydx • In polar coordinates: dA = r drdθ
Ex. Evaluate where R is the region in the first two quadrants bounded by x2 + y2 = 1 and x2 + y2 = 4.
Ex. Find the volume of the solid bounded by z = 0 and the paraboloid z = 1 – x2 – y2.
Ex. Find the volume that lies under , above the xy-plane, and inside the cylinder x2 + y2 = 2x.